Support Octavia layer2 connectivity between LB and members

We have added support for Octavia with the octavia-support blueprint. However, that's only for when the services and pod subnets are routed. This means that communication between service and pods will have to go through the router, which depending on the SDN is suboptimal.

This blueprint calls for adding a configuration option that allows the deployment to have each LB add a port to the pod subnet so the routing is unnecessary.